Floating screens for use in liquid storage tanks



April 17, 1962 E. A. REYNOLDS 3,029,971

FLOATING SCREENS FOR USE IN LIQUID STORAGE TANKS Filed Sept. 23, 1959 3Sheets-Sheet 1 INVENTORI EDWARD A. REYNOLDS -/S I) EH4 FIG. 4

HIS ATTORNEY April 1962 E. A. REYNOLDS 3,029,971

FLOATING SCREENS FOR USE IN LIQUID STORAGE TANKS Filed Sept. 25, 1959 3Sheets-Sheet 2 FIG. 5

INVENTORI EDWARD A. REYNOLDS #DBWLL HIS ATTORNEY April 17, 1962 E. A.REYNOLDS FLOATING SCREENS FOR USE IN LIQUID STORAGE TANKS Filed Sept.25, 1959 3 Sheets-Sheet 3 FIG.

INVENTORI EDWARD A. REYNOLDS BY: HIS ATTORNEY 3,029,971 FLOATING SCREENSFOR USE IN LIQUID STORAGE TANKS Edward A. Reynolds, Ightharn, Kent,England, assignmto Shell Oil Company, New York, N.Y., a corporation ofDelaware Filed Sept. 23, 1959, Ser. No. 841,782 Claims priority,application Great Britain Sept. 29, 1958 1 Claim. (Cl. 220-26) Thepresent invention relates to floating screens or partitions for use inliquid storage tanks. When storing either volatile liquids (eg.gasoline) or liquids having volatile components (eg crude oil), inexposed storage tanks such as those employed in the tank farms of oilrefineries and other oil-handling installations, considerable lossesoccur due to the expulsion of vapor through the tanks venting valveswhich are arranged to prevent the build-up of dangerously high vaporpressures within the tanks. These losses may occur for example onheating of a tank during the day, or an expulsion of vapor due tofilling of the tank with liquid. Naturally they are greatest in a hotclimate.

it has been proposed to reduce these losses by providing liquid storagetanks with floating screens which lie in or on the surface of the liquidand cover the majority of the liquid surface, limiting the surface areafrom which evaporation can occur. Particular proposals include theprovision of floating screens of metal foil or flexible sheets ofsynthetic resin material.

It is an object of the present invention to provide an improvedconstruction for such screens, important factors being ease of assemblyof a screen in situ within a tank and simplicity and hence reduced costof manufacture.

According to the present invention a floating screen for use in a liquidstorage tank comprises a plurality of sections assembled to form ascreen shaped to cover the majority of the surface or" liquid stored inthe tank, each section being formed from two flexible sheets joined ator near their edges to form an airtight pocket or chamber so as torender the section buoyant, adjoining sections each having at least oneof its sheets formed at the adjoining edge into a flange projectingupwards and inwards over the section, whereby the inward projection ofthe flanges of adjoining sections provide a broadening around or onwhich one or more sleeve fastening means are placed to secure thesections together. The flange comprises a lower substantially verticalportion adapted to abut against the corresponding portion on an adjacentsection, and an upper portion which projects or has a part projectinginwards over the surface of the section but does not project outwardsbeyond said lower portion.

Usually the screen will be shaped to fit within the tank for which it isintended with a small clearance between its edge and the walls of thetank, a flexible sealing collar or the like which makes rubbing contactwith the walls of the tank being provided around the edge of the screento seal the gap. it is usually convenient also to have a separatecentral sheet which may be supported by the remainder of the screen.

In one arrangement of a screen according to the present invention foruse in tanks of circular horizontal crosssection, the sections of thescreen, apart from a central circular section, are arranged to form oneor more concentric annuli, each annulus being made up of a number ofsections formed by dividing the complete annulus into a number of equalsectors. in particular the annuli, except for an outer edge annulus ofcomparatively narrow radial width, may be subdivided so that the lengthof of the outer arcuate ends of all the sections is approximately thesame regardless of which annulus they form part, this length beingdetermined so that the sections can pass through the manholes providedon a tank. The radii of the outer edges of the annuli may be determinedto correspond to various standard tank diameters so that standardsections may be manufactured for use in tanks of several diameters. Thesections in the different annuli are arranged so that the radial joinsin one annulus do not, as far as possible, lie opposite those in theneighboring annuli. The sections of the outermost annulus will usuallybe provided with means for mounting on it a flexible collar for sealingthe gap between the edge of the screen and the tank wall.

In another form of screen according to the present invention there maybe a plurality of sections of identical shape and size, the shape beingthat of an equilateral triangle, a square, a rhombus or a regularpolygon having an even number (preferably six or eight) of sides, thesesections being assembled in a honeycomb pattern and constituting thewhole or only a major part of the screen. In the majority of cases whichincludes all tanks of arcular cross-section, the honeycomb patterncannot fit the shape of the tank and additional sections of differentshapes have to be included to form the outer edge part and in some casesalso the center part of the screen. Some of these additional sectionsmay conveniently have a shape which is a part of the shape of thesections forming the honeycomb pattern and is formed by omitting thepart to one side of a line joining two non-adjacent corners.

An example of a floating screen according to the present invention foruse in a liquid storage tank will now be described with reference to theaccompanying drawing in which:

FIG. 1 shows a plan view of a screen illustrating an arrangement of thesections in a circular screen;

FIG. 2 shows a cross-section through the adjoining edges of two sectionsof the screen shown in FIG. 1;

FIGS. 3 and 4 show respectively a plan view of a part of the screenwhere three sections meet and a perspective view of an elementincorporated at that point;

FIGS. 5 and 6 show separate perspective views of two trays whichtogether form a section;

FIG. 7 shows a similar perspective of the trays of FlGS. 5 and 6 whenassembled;

FIG. 8 shows a section at 8-8 in HS. 7;

FIG. 9 shows a perspective view of a part of the edge of the screen inposition in a tank; and

FIG. 10 is a similar view to FIG. 2 showing a modification.

Referring to FIG. 1 it will be seen that the screen which in thisspecific example is designed for a tank of 48 ft. diameter, includes acentral section 1 which is surrounded by four successive concentricannuli 2-5 and an outer edge annulus 6. The diameters of the successiveperimeters of the section 1 and annuli 2-6 are, in order, 3, 13, 23, 33,46 and 48 ft. These diameters are chosen, apart from the first and thelast one, as being in each case 2 ft. less than a standard tankdiameter, so that by adding an edge annulus, 1 ft. wide and ofappropriate diameters to only the appropriate part of the screen shownin FIG.

l, a screen for tanks of 15, 25 and 35 ft; diameter can be formed. Byproviding additional annuli with inner and outer diameters of 46, 54 and62 ft, tanks of 48, 56 and 64 ft. diameter can be covered and the annulifor this whole range of tanks is standardized. A diflerent series ofannuli of inner and outer diameters of 14, 18, 28 and 38 ft. can be usedto cover the range of tanks of 15, 20,

30 and 40 ft. diameter.

Each of the annuli 2-5 (it is to be understood that each case so thatthe length of the chord extending across the wider arcuate end of thesections is in all cases less than the diameter of the manholes providedon the tanks for which the screens are intended, so that the sections ofa screen can be passed into the tanks and assembled in situ. Often thesemanholes are 2 ft. 6 ins. in diameter so that the chord width mayconveniently be about 2 ft. or 2 ft. 3 ins. In addition, when assemblingthe screen, it is arranged as far as possible that radial joins in theannuli do not lie opposite those in adjoining annuli.

FIG. 2 shows a vertical section through the adjacent edges of twosections of the screen, the arrangement being as shown whether the edgesare circumferential or radial edges. Each section is formed by two traysand 11 each constructed of a flexible plastic sheet material, such forexample as polyvinyl chloride or polyethylene, only parts of the trays1t and 11 of the two sections appearing in FIG. 2 being shown. The edgesof the upper trays 10 are turned upwards to form flanges 12 having anupper portion 12a which in section is semicircular apart from a smalldownwardly projecting lip 12!) on the upper edge of the portion 120. Thelower trays 11. slope upwards towards their edges and then terminate invertical flanges 13 the inner surfaces of which are cemented to theouter surfaces of the flanges 12 on the upper trays 10, the cement beingindicated by the shaded areas 14. The two trays 10 and 11 of eachsection are joined in this manner right round their edges so that thespace between them forms an air-tight pocket rendering the sectionbuoyant when placed on liquid. When two sections are placed side byside, the upper flange portions 121: of the upper trays 10 together forma tubular broadening of the upper edges of the flanges 12, around whichis sprung a sleeve fastener 15. The fasteners extend along the wholelength of the edges of the sections apart from short breaks at thejunctions where three sections of the screen are contiguous. A smallclearance space of for example A1, is left between the outer faces ofthe flanges 13 of neighboring sections.

FIG. 3 shows a plan view of a point where three sections are contiguous,two of them being section 3.3 of the second annulus and one a section 2sof the first annulus. The ends of three fasteners 15 are shown eachterminating short of the junction. A solid or tubular plastic T- piece16 (see FIG. 4) is inserted inside the upper flange portions 12a to sealthe gap that would otherwise occur. The lips 12b may be removed for thedistance that piece 16 projects into the flange portions 121! or piece16 may be provided with grooves to accommodate the lips 12]). A moldedpress-on cover could be provided as an alternative to piece 16.

A preferred form of construction of the trays 10 and 11 is shown inFIGS. 5-8. FIG. 5 shows a perspective view of the upper tray 10,including the flange 12. the main surface 17 of the tray 10 slopingdownwards from all points to a circular flat or level portion 18 ofsmall area. FIG. 6 shows the corresponding view of the lower tray 11with its flange 13, a central boss 19 being mounted (for example it maybe molded integrally with the tray 11) on the upper surface of tray 6 ina position such that it lies directly under the flat 18 on the tray 10when the two trays 1t} and 11 are assembled together. The upper surfaceof the boss 19 is the same area as the flat 1S and lies in contact withor close to the flat 18 when the trays 1t"! and 11 are loosely fittedtogether. A metal drainage unit comprising a tube 2.0 with a flange a(see FIG. 7 which shows the trays 10 and 11 together) at one end ispassed through the corresponding holes 13:: and 19a in the flat 18 andthe boss 19 respectively. FIG. 8 is a section at 88 in FIG. 7 and showsthe juxtaposition of the flat 18 and the top of the boss H, togetherwith the drainage unit, the tube 26 of which provides a passage enablingliquid collected on the upper surface of the tray 10 to run through tothe underside of the screen.

If required two or more bosses 19 and flats 18 may be provided on thesame section of the screen, each having a draining unit. Besidesallowing provision for drainage, the bosses 19 add to the rigidity ofthe sections, and Without them it will usually be necessary to providesome other strengthening such as lattice of struts which fits within thespace between the trays 10 and 11.

FIG. 9 shows a part of the edge of the screen assembled in a tank, partof the wall 25 of which is shown together with the liquid surface 26.Parts of two sections 5s are shown assembled and joined along theiradjacent radial edges by a sleeve fastener 15. Also shown are parts oftwo sections 6s of the outer edge annulus which are about 1 ft. in width(radially) and 3 ft. in length. These sections 65 are constructed of thesame material as the remainder of the screen and each includes a sheet30 provided on its inner circumferential edge with a flange 31 identicalwith the flanges 12 on the sections 2s--5s. As shown in FIG. 9, theflanges 31 are joined to the flanges 12 on the adjoining edges of thesections SS in the usual manner with sleeve fasteners 15. The radialedges 32 of the sections 6s simply overlap, and the outercircumferential edge is provided with a short upstanding flange 33 about1 inch high. To render the sections 65 buoyant, air pockets are formedby attaching (by cementing or by welding) pocket pieces 34 to theunderside of the sheet 30.

The sections 6: each carry a part of a sealing collar 49 of known formwhich makes rubbing contact with the wall 25 of the tank to seal the gapbetween the edge of the screen and the wall 25. The sections of thecollar 40 are constructed of corrugated sheet material, each sectionhaving a base 41 which is some 10 wide and is bolted to the uppersurface of the sheet 3 of the section 6s on which it is mounted, avertical wall 42 some 8" high and an upper horizontal flange 43 about 3"wide which projects radially beyond the periphery of the section 6s andrubs against the tank wall 25. The wall 42 is formed with gussets 44 forstiffening purposes. Corrugations on the sheet material used forconstucting the collar may be provided for stiffening purposes and couldrun circumferentially being about Vs deep and spaced about /z" apart.The material used will usually be the same as that employed for the restof the screen. The ends of the sections of the collar .9 overlap in thesame way as the screen sections 6s on which they are mounted.

FIG. 10 is a similar view to that of FIG. 2 and shows a stiffener 22mounted between the upper flange portions 12a to support them againstthe clamping pressure of the fastener 15. The stiflener 22 may be aplastic tube and may extend the same length of the flange portions asthe fastener 15.

In an alternative arrangement, in order to standardize as far aspossible the shape of the sections to be employed in screens ofdiflerent sizes, use is made of sections having some regular shape forexample square, rhombus or the shape of a regular hexagon. Apart fromtheir shape, these can be constructed and joined in exactly the same wayas the sections of the screen described with reference to the drawing.They are fastened together in a honeycomb pattern to form the majorityof the screen for tanks of a variety of shapes and sizes. Apart from thecase of square sections in a square or rectangular cross-section tank,the screen will usually have to be completed around its edge by an outeredge part the shape of which is somewhat irregular, but which isconstructed in a similar manner to the edge annulus 6 of the screenshown in the accompanying drawing. To reduce the irregularity of theedge part, use may be made of sections the shape of which is aconvenient part of the shape of the sections forming the honeycomb. Thuswhere the honeycomb is formed of sections in the shape of a regularhexagon, sections having a shape formed by dividing the hexagon across adiagonal or across a line joining two corners spaced apart by one corneronly can conveniently be incorporated in the screen to make the edge ofthe honeycomb more regular in shape.

It is particularly envisaged that this last construction may be employedfor screens for use in new tanks under construction so that no limit isplaced on the size of the sections by the need to pass them throughexisting .manholes, the screen being assembled before the tank roof isapplied. For example, hexagonal sections measuring 4 feet across adiagonal may be used. The use of such large sections will beparticularly convenient in large tanks.

In the screens described above, use has been made of sections of certainconvenient shapes and constructed in particular ways of variousmaterials. It will be appreciated, however, that construction of screensaccording tov the present invention is not limited to these examples. Inparticular, sections of other shapes may be found convenient in tanks ofsome particular shape, while the construction of the trays may be variedin detail while retaining the basic principles that they include twoflexible sheets joined at or near the edges to form an airtight pocketand have a suitable flange. Any sheet material may be used provided itis impermeable to liquid and chemically resistant to the liquid to bestored in the tank, and amenable to being formed to the desired shape.For example, other synthetic plastics or resins with or without fibrousor other reinforcement may be employed, or metallic sheets which mayhave a thin plastic or resinous coating may be used.

While the provision of one or a smallnumber of bosses 19 (FIGS. 6 and 8)is preferred for strengthening each section, otherstrengtheningstructures may be incorporated if desired. For example, alattice of strips with their major surfaces vertical and of width equalto the The combination with -a storage vessel for volatile v liquids,the vessel having an upright wall of: a flexible blanket comprisingmultiple plastic cellular float units,

' each float unit comprising an upper dished plastic section and a lowerdished plastic section, said plastic sections being so formed that uponassembly said sections fit together along their peripheral edges to forma unitary hollow structure, each said float unit being provided with anintgeral flange at its upper edge, said flange projecting upward fromsaid edge to form a substantially vertical wall portion, and continuingfrom the top of said vertical wall portion in the form of an inwardlyextending head of substantially semicircular cross-section, whereby thebeads of two adjacent float units define a hollow tubular top rim; acylindrical reenforcing member fitting snugly in the hollow of said toprim between two adjacent float units, and a split tubular clampingsleeve fitting snugly over said tubular top rim and resiliently pressingsaid beads against said cylindrical member to firmly retain two adjacentfloat units joined together while permitting a limited amount of angularplay between said joined units.

I References Cited in the file of this patent UNITED STATES PATENTS FinoDec. 29, 1959

